Why is there no cure for cancer yet.

Too broad. The cause of cancer is due to gene mutation. What causes the mutation in a particular gene that causes a particular cancer is the modern question for cancer prevention. Each cancer is different so "curing cancer" is a broad statement and involves understanding the cause of gene mutation for that particular type.
Very complex illness. Thank you for that question. Cancer is an extremely complex illness. There are also all kinds of cancer, each of which has its own nature and risk factors. Some cancers have a better chance of being cured than others, especially when found early. I personally know people who have overcome breast cancer, leukemia, sarcoma, and other cancers. We also have more work to do.